CVE-2022-0850: Linux Kernel Information Disclosure Flaw

CVE-2022-0850 Overview

A vulnerability was discovered in the Linux kernel where an information leak occurs via ext4_extent_header to userspace. This flaw allows a local attacker with low privileges to potentially extract sensitive kernel memory contents, leading to information disclosure that could be leveraged for further attacks or system compromise.

Critical Impact

Local attackers can exploit this vulnerability to leak sensitive kernel memory information through the ext4 filesystem extent header, potentially exposing cryptographic keys, memory addresses useful for bypassing ASLR, or other privileged data.

Affected Products

• Linux Kernel (multiple versions)
• Systems using ext4 filesystem
• Red Hat Enterprise Linux and derivatives

Discovery Timeline

• 2022-08-29 - CVE CVE-2022-0850 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-0850

Vulnerability Analysis

This vulnerability is classified as an Information Exposure issue (CWE-200) affecting the Linux kernel's ext4 filesystem implementation. The flaw exists in the handling of ext4_extent_header structures, where improper data handling allows kernel memory contents to leak to userspace processes.

The ext4 filesystem uses extent trees to efficiently map file data to disk blocks. The ext4_extent_header structure is used internally to manage these extent trees. Due to improper initialization or boundary checking in the affected code path, portions of kernel memory that should remain protected can be inadvertently copied to userspace, allowing an unprivileged local user to read sensitive kernel data.

This type of information leak vulnerability can be particularly dangerous as it may expose kernel address space layout information, which attackers can use to bypass Address Space Layout Randomization (ASLR) and craft more sophisticated exploits targeting other kernel vulnerabilities.

Root Cause

The root cause of this vulnerability lies in improper handling of the ext4_extent_header structure during filesystem operations. Specifically, uninitialized or improperly sanitized memory regions associated with extent header data are being exposed to userspace, violating the kernel-userspace security boundary.

The vulnerability was identified through automated fuzzing using the Syzkaller kernel fuzzer, as documented in the Syzkaller Bug Report #78e9ad0.

Attack Vector

The attack requires local access to the system with low privileges. An attacker would need to:

1. Gain local access to a system running a vulnerable Linux kernel version
2. Interact with the ext4 filesystem through standard system calls
3. Trigger the vulnerable code path that handles ext4_extent_header structures
4. Extract leaked kernel memory information from the returned data

The vulnerability is exploitable without user interaction, though it requires local system access. The attack does not allow direct code execution but compromises confidentiality and may affect system availability.

For detailed technical analysis of the vulnerability mechanism, refer to the Linux Kernel Commit ce3aba4 and the Red Hat CVE-2022-0850 Advisory.

Detection Methods for CVE-2022-0850

Indicators of Compromise

• Unusual access patterns to ext4 filesystem metadata from unprivileged processes
• Suspicious system calls targeting extent header operations repeatedly
• Processes attempting to read filesystem structures beyond normal application behavior
• Memory access anomalies related to ext4 filesystem operations

Detection Strategies

• Monitor for abnormal system call patterns involving ext4 filesystem operations using tools like strace or eBPF-based monitoring
• Deploy kernel-level auditing with Linux Audit System (auditd) to track filesystem-related syscalls
• Implement SentinelOne's Singularity platform for real-time behavioral analysis and kernel-level threat detection
• Review system logs for indicators of repeated filesystem metadata access attempts

Monitoring Recommendations

• Enable comprehensive kernel logging to capture filesystem operation anomalies
• Configure alerting for unusual process behavior patterns involving filesystem metadata access
• Utilize SentinelOne's Storyline technology to correlate suspicious filesystem activities across the attack timeline
• Regularly audit system call patterns from potentially compromised or suspicious processes

How to Mitigate CVE-2022-0850

Immediate Actions Required

• Update the Linux kernel to a patched version that includes commit ce3aba43599f0b50adbebff133df8d08a3d5fffe
• Apply vendor-specific security updates from your Linux distribution
• Review and restrict local access to systems running vulnerable kernel versions
• Monitor for unusual filesystem activity while awaiting patch deployment

Patch Information

The vulnerability has been addressed in the upstream Linux kernel. The fix is available through Linux Kernel Commit ce3aba4. Red Hat has provided guidance and tracking information through Red Hat Bug Report #2060606.

Organizations should apply kernel updates from their respective Linux distributions, which incorporate the upstream fix. For Red Hat-based systems, consult the Red Hat CVE-2022-0850 Advisory for specific package versions containing the fix.

Workarounds

• Restrict local system access to trusted users only until patches can be applied
• Implement additional access controls using SELinux or AppArmor to limit filesystem metadata access
• Consider temporarily restricting access to ext4 filesystem operations for non-essential user accounts
• Deploy additional monitoring and alerting for filesystem-related anomalies as an interim measure

# Check current kernel version
uname -r

# Verify if your system has the patched kernel
# (Check your distribution's security advisories for specific version numbers)

# Enable additional ext4 filesystem auditing
auditctl -w /sys/fs/ext4/ -p rwxa -k ext4_monitor